I like those ideas, but I'm a little cautious. I like the idea of steam technology spreading with the years, and I feel like the industrial region winning is the only way to accomplish that. At the same time, it seems strange that an agrarian region would rely on automatons and still be noticeably different from an industrial region. Also, will the setting be too radically different from the real world if the agrarian nation wins? Let's work through this stuff.
Big Ideas behind the war: ensuring the freedom that brought the Empire to these shores in the first place, and the fight to recognize the worth of all (Imperial?) sentience?
SpoilerRL New Orleans was allied with the South, but got itself swiftly occupied by the Union in short order. Personally? I'd make Coterois into this world's Casablanca, a place that, during the war, acted with great autonomy due to its remoteness, acting as both City of Spies and gateway out of a war-torn nation. During the war, Coterois was of great strategic importance (it was hard to chase smugglers into the swamps and its sailors were experienced enough to run blockades with ease), that it was the unoffical middle ground, where agents of the North and South could meet, both for diplomatic purposes, espionage and occasionally assassination. After the war, the city became a safe haven for deserters and veterans alike, particularly the more violent element who couldn't let go of the carnage they saw.
That idea is just. too. cool! I'm totally down with it. Maybe with a dash of this? Off the top of my head, I can't think of anything cooler than Steampunk Noir Zombies in the Wild West.
SpoilerNothing so far beyond that Poe idea. I'll think on it.
Think harder!
On another note: the double-action revolver wasn't developed until the 1880s, which limits people in our world from going rapid-fire mode unless they're REALLY good, which I like. There's also an implication that you can shoot faster if you're only holding one gun. Alternately, you could have two guns, shoot less often, but have two different enhancements at your disposal. I like these ideas.
I also watched Sukiyaki Western Django tonight, and it restored my faith in the ability to have guns and sword side-by-side. Wunderbar!